1. Field of the Invention
The present invention relates to a sand core assembly for casting metal parts.
2. Background Art
Metal casting is a technique that may be used to form complex parts. The parts may be formed from ductile iron, aluminum or other metals. Examples of ductile iron castings include engine crankshafts, valve camshafts, engine blocks and other parts.
Conventional core boxes are generally formed with a clamshell design having two halves that are split longitudinally at a parting line. One problem with conventional core boxes and in particular with regard to core boxes for casting crankshafts is that it is difficult to maintain dimensional accuracy in the final cast part. Conventional cast crankshafts require substantial machining to form a flange hub pilot hole, oil gallery passages and shape counter-weights. In conventional core boxes a three degree draft angle is provided on counter-weight cheeks and substantial machining or “cheeking,” is required to eliminate the draft angle. It is also necessary to drill pilot holes and oil gallery passages in the crankshaft casting.
Another problem with conventional casting processes is that the cast parts generally must be homogeneous as cast and do not permit selectively weighting portions of counter-weights with dissimilar materials without further machining and assembly.
Conventional casting also results in flash being formed that must be removed in a cleaning process and consequently adds expense to the casting process. Molding parting lines may also interfere with machining operation clamping points.
Machining variations can also cause problems relating to balancing the crankshaft. Normally, a window is provided as to the degree of balance of the shaft that is acceptable. The window is reduced when it is necessary to account for machining variation.
A need exists for a casting process for a complex rotatable shaft, such as a crankshaft or a camshaft. There is also a need for a casting process wherein the complex shaft can be formed accurately with no draft, and including “as cast” oil galleries and other features. A process is needed wherein a core may be inserted into a cope/drag core package allowing for a no-flash mold line without green sand. There is also a need for a process utilizing a unitized core package that may be easily integrated into a robotic or automatic system. Finally, there is a need for a core that may be used to make complex shafts that vents well and produces fewer casting gas inclusions.
The above problems and long felt needs are addressed by Applicant's invention as summarized below.